I don't allow my XC runners to go to the gym unless I am with them. They always make friends with some beach buf knucklehead and do cut down sets to build muscle mass but not strength.
They will argue to me about this like I don't know what I'm talking about. This is not even good for my sprinters.
Every pound you put on your body you have to fight vertical forces to support. Upper body weight I the death of runners. Even sprinters. Arm movements can not lift the body mass you produce in the weight room against gravity. That's a fact.
Almost nobody is lifting correctly in regards to the needs of runners.
Distance runners are usually the type of the people whom needs to work hard to gain more muscle mass. Sprinters are very different, and they aren't in a glycogen depleted state. You can look more muscular easily by strength training but that doesn't necessarily mean that you've gained more muscles. Among with this distance runners are almost always in a glycogen depleted state, so it's very hard to build muscles so much that it effects negatively to your running.
Did Sebastian Coe lift correctly? My point just is; is that really that complicated?